Pupillary reflex enhanced by light inside blind spot

June 30, 2015, University of Tokyo
Pupillary light reflex in response to light stimuli inside and outside the blind spot. Left: Relationship between the blind spot and the optic disk. Right: summary illustrations of results. In each panel, white and blue lights indicate the light stimuli presented outside and inside the blind spot, respectively. Credit: Ikuya Murakami

University of Tokyo researchers have found that the light reflex of the pupil is modulated by light stimulation inside the blind spot in normal human observers, even though that light is not perceived.

The human retina contains some 100 million photoreceptor cells. When these are stimulated with light, they communicate that information to the brain and we perceive light. However, the optic nerve and blood vessels pass through the region of the retina called the optic disk, which contains no photoreceptors. Light falling on this blind spot is therefore never consciously seen. On the other hand, if a donut-shaped ring of light is targeting to the area around the blind spot, we perceive it as if light were present inside the blind spot itself as well.

When light falls on the eyes, pupil constriction, called the pupillary light reflex, reduces the pupil diameter with less than one second latency. It is known that the pupillary light reflex depends on the area of impinging light. However, the relationship between the light area and the pupillary light reflex remained unclear in the case of the blind spot, where the physical and perceived light areas were different from each other.

Japan Society for the Promotion of Science Postdoctoral Fellow (PD) Kentaro Miyamoto at the Graduate School of Medicine, and Associate Professor Ikuya Murakami at the Department of Psychology, Graduate School of Humanities and Sociology, discovered that when light impinges on the photoreceptor-free blind spot alone the pupillary reflex does not occur, but the pupillary reflex is enhanced in response to bright illumination in a normal part of the retina when blue or white light containing shorter wavelengths is simultaneously delivered inside the blind spot.

One possible explanation for these seemingly contradictory results is that the blind spot contains the axons of , especially those that are intrinsically photosensitive. Thus, it is proposed that neural signals originating from light reception at photoreceptors are modulated by light reception in these ganglion cells.

Taking advantage of the unique place occupied by the blind spot will make it possible for researchers to further elucidate the processes underlying adaptive controls in response to light stimulation onto the retina, including pupillary reflex and circadian rhythm. "Future research will be directed at possible influences of stimulation on conscious or unconscious visual decision processes, and thereby toward the understanding of multiple information processing tracks in the brain," says Associate Professor Murakami.

Explore further: Retinal cells thoughts to be the same are not: study

More information: "Pupillary light reflex to light inside the natural blind spot", Scientific Reports 2015/06/26: Online Edition, DOI: 10.1038/srep11862

Related Stories

Retinal cells thoughts to be the same are not: study

July 25, 2011
The old adage "Looks can be deceiving" certainly rings true when it comes to people. But it is also accurate when describing special light-sensing cells in the eye, according to a Johns Hopkins University biologist.

Newly developed chemical restores light perception to blind mice

February 19, 2014
Progressive degeneration of photoreceptors—the rods and cones of the eyes—causes blinding diseases such as retinitis pigmentosa and age-related macular degeneration. While there are currently no available treatments to ...

Brain control? Shining light on pupil constriction

November 2, 2011
(PhysOrg.com) -- You’ve seen it on television: A doctor shines a bright light into an unconscious patient’s eye to check for brain death. If the pupil constricts, the brain is OK, because in mammals, the brain controls ...

New stem cell approach for blindness successful in mice (w/ video)

January 8, 2013
(Medical Xpress)—Blind mice can see again, after Oxford University researchers transplanted developing cells into their eyes and found they could re-form the entire light-sensitive layer of the retina. 

Recommended for you

How do we lose memory? A STEP at a time, researchers say

March 23, 2018
In mice, rats, monkeys, and people, aging can take its toll on cognitive function. A new study by researchers at Yale and Université de Montréal reveal there is a common denominator to the decline in all of these species—an ...

Brain's tiniest blood vessels trigger spinal motor neurons to develop

March 23, 2018
A new study has revealed that the human brain's tiniest blood vessels can activate genes known to trigger spinal motor neurons, prompting the neurons to grow during early development. The findings could provide insights into ...

Being hungry shuts off perception of chronic pain

March 22, 2018
Pain can be valuable. Without it, we might let our hand linger on a hot stove, for example. But longer-lasting pain, such as the inflammatory pain that can arise after injury, can be debilitating and costly, preventing us ...

From signal propagation to consciousness: New findings point to a potential connection

March 22, 2018
Researchers at New York University have discovered a novel mechanism through which information can be effectively transmitted across many areas in the brain—a finding that offers a potentially new way of understanding how ...

Using simplicity for complexity—new research sheds light on the perception of motion

March 22, 2018
A team of biologists has deciphered how neurons used in the perception of motion form in the brain of a fly —a finding that illustrates how complex neuronal circuits are constructed from simple developmental rules.

Focus on early stage of illness may be key to treating ALS, study suggests

March 22, 2018
A new kind of genetically engineered mouse and an innovation in how to monitor those mice during research have shed new light on the early development of an inherited form of amyotrophic lateral sclerosis (ALS).


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.